Multimedia broadcast/multicast services over wireless networks, such as cellular radio networks are becoming widely spread, especially after that mobile handheld devices have become capable of receiving multimedia content via radio networks. However, delivering multimedia over a wireless channel to handheld devices has proven to pose a number of problems. For example, subscribers may experience different channel quality while receiving the same content. In addition, each user wants the highest possible quality of the media.
Layered and scalable codecs have been developed that enable adaptation of the broadcast/multicast stream to changing network conditions. A layered media consists of a base layer and a number of enhancement layers each providing quality refinement for the lower layers. The base layer usually carries the minimum information required by the decoder to provide a minimum quality for the receivers. Each additional layer may refine this minimum perceived quality by, e.g., raising the played out frames per second or extending the screen resolution.
Furthermore, smart bandwidth adaptation can be achieved by forwarding only the layers that are transmittable by altered network conditions. Also, layered media allows the network to handle a number of heterogeneous receivers in the same session having, e.g., different display sizes.
In spite of the existence of these codecs, the adaptation of multimedia flows has to be supported by delivery technologies and access networks as well.
Now, the necessary functions to support Multimedia Broadcast Multicast Service (MBMS) transmission in E-UTRAN also sometimes referred to as Long Term Evolution (LTE) networks are being discussed and defined in the 3GPP standardization body. An important difference compared to the MBMS service delivery in UTRAN comes from the distributed nature of the E-UTRAN architecture. In E-UTRAN the radio resource management functions, including the scheduling are located in the evolved Node Bs (eNodeBs), i.e. in the base stations as opposed to UTRAN, where the radio resource control is located centrally in the Radio Network Controller (RNC). Therefore, for MBMS transmission, which may require coordinated and time synchronized transmission from multiple cells (also called Single Frequency Network, i.e., Single Frequency Network (SFN) or Multi Broadcast Single Frequency Network (MBSFN), transmission); additional central control entities have been added to the architecture. A currently proposed MBMS architecture is depicted in FIG. 1.
In FIG. 1 BM-SC is the Broadcast Multicast Service Center, which is the application level server providing the multimedia content. The MBMS Gate Way (GW) is responsible for the user plane processing of the MBMS data, including such functions as content synchronization and delivering the data over a multicast IP transport to the relevant eNodeBs. The MBMS GW also executes control over the start and stop of the services and acts as a mediator between the access agnostic multimedia content sources and the LTE specific access network.
The MBMS Control Entity (MCE) is a radio resource control entity, which is responsible mainly for the coordinated allocation of radio resources over multiple cells in case of SFN transmission mode.
Currently the standard defines three main transmission methods to deliver MBMS content in LTE networks. These are:
Single Frequency Network (SFN) Transmission:
In this transmission mode, the same multimedia content is transmitted in multiple cells in a time synchronized fashion such that the physical signals arriving from different cells at the User Equipment (UE) can be soft-combined.
Single Cell PTM (Point to Multipoint) Transmission Without Feedback:
In this mode the transmission in a cell is targeted only for the users in the given cell. In other words, there is no coordination of the transmission from multiple cells. This also means that a particular eNodeB on its own can control the radio resources the eNodeB spend on the MBMS transmission, i.e. it is able to perform scheduling. No feedback information is available from the UEs regarding the link quality, success/failure of the reception.
Single Cell PTM Transmission with Feedback:
This mode is the same as Single Cell PTM transmission with the possibility of sending feedback information from the UEs regarding the link quality and/or the success/failure of the reception. Utilizing feedback information from the UEs can help to optimize the transmission accordingly and thereby utilize the radio resources more efficiently.
For the transport of MBMS data over the radio interface the standard currently defines the MCH transport channel, capable of SFN transmission and the MBMS Control Channel (MCCH) and the MBMS Traffic Channel (MTCH) logical channels. The MCCH and MTCH logical channels are mapped onto the MCH transport channel. Optionally, it may be possible to map these logical channels to the normal downlink shared channel (DL-SCH) used to deliver the unicast traffic as well. This may be possible in the single cell transmission cases, when the SFN transmission mode is not used and therefore the MCH transport channel can be omitted. The MTCH channel carries the actual MBMS data. The MCCH channel carries control information necessary for the reception of the MTCH channel. The MCCH includes session/service identities for sessions to be started, i.e., announcing service starts, identities for ongoing services, scheduling information etc.
Today, there exist a need for a method and a system that is able to improve the performance of an E-UTRAN radio system.